This invention relates to methods for remote detection and more particularly to methods for detecting geologic deposits.
Methods for detecting mineral and petrochemical geologic deposits may be roughly divided into two types: supplied signal methods, in which a signal is both induced and observed at a site of interest and indigenous signal methods, in which a signal is observed, but is not induced at the site of interest. Examples of the former are resistivity studies based on an external voltage applied between two or more buried electrodes, inductive methods based upon changes in inductance of an applied signal at a receiver a short distance away, and nuclear magnetic logging methods based upon nuclear precession in materials adjacent an instrument which supplies a magnetic field. Examples of methods relying on indigenous signals are magnetic field mapping and radioactivity mapping.
A shortcoming of these induced signal methods is that the signals are rapidly attenuated with depth or horizontal distance. This limits the versatility of these methods. Indigenous signal methods often have the shortcoming that the characteristic measured may only distantly correlate with the material sought. This is not the case where, for example, radioactivity measurements are used to search for uranium, but is the case where radioactivity measurements are used to help detect oil and gas deposits.
It is therefore highly desireable to provide an improved method for detecting geologic deposits.
It is also highly desireable to provide an improved method for detecting geologic deposits which relies upon an indigenous terrestrial alternating electromagnetic radiation signal.
It is also highly desirable to provide an improved method for detecting geologic deposits in which an indigenous terrestrial alternating electromagnetic radiation signal, which correlates with the material sought is measured.
It would finally be highly desirable to provide an improved method for detecting geologic deposits which meets all of the above desired features.